ROBERT CHAMBERS 51 



are given in a former paper.^ The cytoplasmic granules, instead of 

 being readily dislocated by the moving needle, are held as in a jelly, 

 and movements of the needle produce torsions of the entire egg 

 substance. This condition is at its height 10 to 15 minutes after 

 fertilization. 



15 to 20 minutes after fertilization, the radiations of the aster 

 begin to fade from view, with a reversal in the cytoplasm of the semi- 

 solid to a more fluid state. The cytoplasmic granules are now easily 

 dislocated by the moving needle. The more prominent radiations 

 disappear first, while the finer ones persist for some time, owing prob- 

 ably to the viscid nature which the cytoplasm always maintains. 

 The liquid substance of the central hyaline area now flows over the 

 nucleus to its two poles, beyond which it often extends. This causes 

 the appearance characteristic of this stage, of a hyaline streak plainly 

 visible in the otherwise granular cytoplasm of the egg. Toward the 

 end of this stage, which lasts for about 20 to 30 minutes, the hyaline 

 substance finally collects into two semispherical masses lying at the 

 two poles of the nucleus. 



Shortly before cleavage, about 40 to 50 minutes after fertilization, 

 an increase in firmness sets in, spreading radially from each of the 

 two centers situated at the poles of the nuclear spindle. This con- 

 stitutes the amphiaster. The egg elongates, the long axis passing 

 through the two centers of the amphiaster. The cleavage furrow 

 now appears and the egg rapidly divides. The time of appearance 

 of the amphiaster until completion of cleavage lasts from 10 to 15 

 minutes. The increased viscosity of the egg during this amphiaster 

 stage could be more easily demonstrated by the needle in the eggs 

 of Echinarachnius and Cerebratulus than in those of Arbacia. 



After completion of the cleavage process, there are indications that 

 the firmness of the cytoplasm persists in the two blastomeres while 

 they are still more or less spherical. Within 10 to 15 minutes after 

 cleavage the two blastomeres crowd up against one another, each 

 assuming a more nearly hemispherical shape. At this stage their 

 cytoplasm is again quite fluid. 



These observations demonstrate a pronounced periodicity in the 

 physical state of the egg subsequent to fertilization and during the 

 first cleavage process. In the immature egg the viscosity is high, 



